The oil pump, oil filter and oil cooler of a hermetic centrifugal chiller can make up a package. The oil is pumped through the filter and cooler to remove foreign particles and excess heat, respectively. A portion of the lubrication oil can be used to position the diffuser wall. Oil flow is directed to the compressor motor end bearing. The remaining oil flow lubricates the compressor transmission, journal and thrust bearings. Oil then drains into the oil reservoir to complete the cycle.
Various types of pumps may be used for circulating the oil depending upon the specific use in view of the suction head, steady state and transient conditions, noise, pressure pulsations, etc. of the specific use. Because refrigerant is in the oil, with the maximum amount being present at startup, the transient conditions of outgasing and foaming can occur in response to the suction pressure drop. In the case of a rotary vane pump the overall performance is good but it is noisy and has pressure pulsations. The pulsations occur at the vane passing frequency which is equal to the number of vanes times the running speed. Pressure pulsations are related to the swept volume per stroke.